In such high-voltage arrangements, the typically used semiconductor switches, which are connected electrically in series, are IGCTs, GTOs, thyristors, MOSFETs and IGBTs, potential isolation being required for supplying power to the gate units in the case of large voltage differences.
Such a potential-isolated power supply for gate units is proposed in WO 02/059628 A.
It is known from the prior art to supply the gate units using respective individual power-supply devices having high potential isolation, either a) by means of highly isolating transformers, connected in parallel with a low-voltage AC bus, usually using 50 Hz technology, or b) by means of separate, highly isolating DC/DC converters, which are connected to a DC voltage supply and are connected in parallel on the input voltage side.
Disadvantages of the known arrangements are, in the case of variant a), the fact that transformers using typical 50 Hz technology are bulky, heavy and expensive, and involve considerable assembly complexity.
In the case of variants a) and b), there are problems with isolation/creepage paths, since the AC or DC power supply bus must run up to each switch stage and be tapped there.
In high-power converter technology, in particular if a series circuit comprising line switching elements is used, increased demands are placed on the isolation of the transformers used in the respective gate control systems and, in particular, also on their parasitic, capacitive coupling between the primary and secondary circuits. This coupling must necessarily be very low in order to prevent the electronic system from having any influence on the gate units owing to charge/discharge currents of the parasitic coupling capacitances. According to the prior art, encapsulated transformers are therefore used to meet the demands placed on isolation. However, these generally have an undesirably high parasitic coupling capacitance, in particular when using transformers based on 50 Hz technology.